This invention relates to semiconductor lasers and more particularly to improvements in phased locked or phased array lasers capable of output beam deflection and scanning in the far field. Examples of monolithic scanning phase locked array lasers including area contract regions are disclosed in Scifres et al U.S. Pat. No. 4,217,561 and Scifres et al U.S. Pat. No. 4,219,785, both assigned to the assignee herein.
Known in the art of phased array lasers comprising a plurality of emitters having with closely spaced injection current stripes to provide for constructive interference between spaced emitters due to the overlap of the evanescent optical fields of adjacent laser emitters. Examples of such phased array lasers are disclosed, for example, in Paoli et al, U.S. Pat. No. 3,701,044 and in the article of Donald R. Scifres et al entitled, "Lateral Beam Collimation of a Phased Array Semiconductor Laser", Applied Physics Letters, Vol. 41(7), pp.614-616, Oct. 1, 1982.
The concept of separately addressing the individual laser strips of a phased array laser to provide for beam steering or scanning is also known on the art and is analogous to phased array radar. However, there exists practical limitations in electrically addressing and modulating closely spaced stripes or emitters because when a group of parallel stripes are placed on 10 .mu.m centers or less, it is difficult, if not impossible, to bond electrical leads to individual stripes without electrical contact to adjacent stripes.
An alternative approach was proposed by Paoli et al, supra, of using a common contact over all of the stripes but breaking the contact into two segments at an angle, as illustrated relative to laser 10 in FIG. 1 herein.
Phased array laser 10 in FIG. 1 comprises a plurality of phase locked emitters L.sub.1, L.sub.2, L.sub.3. . . L.sub.N-1 and L.sub.N, as represented by current confinement stripes 12. The optical cavities of emitters L.sub.1 -L.sub.N extend for the full length L of array laser except their absence in region 18. The pumping of emitters L.sub.1 -L.sub.N is divided into two segments 14 and 16, represented by area metal contacts separated by electrical isolation region 18. The area of strips 12 beneath area contact 14 are pumped by current, I.sub.1, while the area of stripes 12 beneath area contact 16 are pumped by current, I.sub.2. By varying current, I.sub.1, relative to current, I.sub.2, several functional attributes occur. First, because the real and imaginary refractive index of laser 10 depend upon the active region charge density, and because area contacts 14 and 16 area diagonally across emitters L.sub.1 -L.sub.N, the charge distribution profile will vary linearly, i.e., the effective optical cavity length will vary linearly in each pumped segment 14 and 16 from emitter L.sub.1 -L.sub.N. Thus, by varying the relationship of currents I.sub.1 and I.sub.2, different indices of refraction are provided in the regions beneath area contacts 14 and 16 causing a relative phase shifting between emitters that correspondingly causes output beam 11 from laser 10 to deflect or scan in the far field.
Second, variations of current, I.sub.1, relative to current, I.sub.2, will also influence the emission wavelength of laser 10.
Third, such variations of current, I.sub.1, relative to current, I.sub.2, may serve to couple adjacent emitters of laser 10 in phase as opposed to out of phase by 180.degree.. Phased array lasers may generally operate with emitters 180.degree. out of phase, as the favored mode of operation. However, such a mode of operation is undesirable for laser applications, such as raster output scanners or optical disk storage systems, because at least two dominant lobes will be emitted in the far field. A beam with two far field lobes is not useful in these applications.
Thus, while phased array laser 10 does have beam scanning capabilities, it is not easily applied as a beam scanning device since upon variance of I.sub.1 relative to I.sub.2, undesirable variance in mode of operation will also correspondingly occur along with variance in the emission wavelength, which is not acceptable for the above mentioned applications.
Thus, the principal of this invention is to provide a split contact phased array laser which has beam steering capabilities with maintenance of selected emission wavelength and with spatial mode control.